Method and apparatus for humidification of breathable gas with profiled delivery

ABSTRACT

A method and apparatus for delivering breathable gas to a user includes a humidifying unit that is controllable to humidify the gas in accordance with a variable humidity profile such that the gas is delivered to the user at variable humidity levels, e.g., during a treatment session.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 11/658,336, filed Jan. 24, 2007, which is the U.S. national phase of international application PCT/AU2005/001156, filed Aug. 3, 2005, which designated the U.S. and claims the benefit of U.S. Provisional Application No. 60/599,864, filed Aug. 10, 2004, each of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Many humidifiers that are currently manufactured for patient respiratory disorders such as Obstructive Sleep Apnea (OSA) are large, bulky, and have large water reserves to treat most medical-related ailments such as dryness that may be caused by mouth leaks for example. Mouth leaks or any leaks for that matter release humidified gases to the atmosphere and bypasses the patient's airways where it is required. These heavy requirements including those medical conditions requiring high levels of continuous humidification may require humidifier devices with reserves as high as 600 mL of water. This increases the overall size and bulk of the Continuous Positive Airway Pressure (CPAP) Apparatus, ventilator, patient breathing air system, or gas supply system.

Where patients do not exhibit these inadvertent leaks or are only seeking lower levels of humidification, they are likely to be left with an unnecessarily oversized reservoir of remaining water at the end of a treatment session.

Furthermore, there are a substantial number of patients that only require relatively smaller amounts of humidification to marginally improve comfort to an acceptable level for a typical patient. These patients for example may include those that only use their conventional humidifiers (ResMed HUMIDAIRE™ or Fisher & Paykel HC 100™) during the cooler months in winter for small but substantial gain in comfort by adding warmth and/or moisture to the airways that may dry due to the flow of air through the patient airways.

Current humidifiers are generally designed to fulfill the worst ailments and therefore require substantial humidification requirements. These systems could be regarded as ‘overkill’ for a substantial population of OSA patients who are only looking for a ‘comfortable’ level of improvement to undesirable dry and cool air.

Current and conventional humidification systems generally supply a continuous level of humidification as set by the user and dependent on the ambient temperature and humidity level. There are also systems that may modify humidification levels using a number of sensor arrays such as temperature sensors and/or humidity or flow sensors in aid to maximize efficiency and/or synchronize with pressure or airflow. These conventional systems can maximize the performance of the humidifier by being able to deliver the maximum amount of humidity whilst reducing or eliminating condensation (e.g. cooler air can carry less moisture), also known in the art as “rain-out”. However, these types of sensor systems are complex and costly and still consume large amounts of water.

Accordingly, a need has developed in the art to address at least one of the shortcomings of the prior art humidifiers described above.

BRIEF SUMMARY OF THE INVENTION

One aspect of the invention to ameliorate the size and design constraints of the conventional humidifier whilst delivering an adequate and comfortable level of humidification whilst consuming/delivering the fluid (e.g. water, core gas vapor, etc.) in an efficient manner (requiring lower liquid reservoir volumes) and delivered according to the patient's needs, which may also be a manually selectable and/or programmable, semi-automated and/or automated delivery profile.

Another aspect of the invention relates to assisting patients looking for limited improvement to breathing comfort. However, the intention is not to replace conventional, continuously heated humidifiers, but rather to provide an additional choice more suitable for certain patients.

Another aspect of the invention provides profiled delivery of humidified gas to a patient.

Another aspect of the invention reduces water or fluid volume required by maximizing efficient use of water, which is a form of ‘rationing’.

Another aspect of the invention aims to improve breathing comfort according to patient selectable profiles in one embodiment.

These and other aspects will be described in or apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a blower according to an embodiment of the present invention;

FIGS. 2 and 3 illustrate sample humidity profiles for a patient's treatment session; and

FIG. 4 schematically illustrates an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a blower 10 according to an embodiment of the present invention. Blower 10 typically includes a housing 12 to support a blower motor 14 that pressurizes breathable gas for delivery to a patient interface 16 (e.g., a mask) via an air delivery conduit 18 that is connected to an outlet conduit 20 of blower 10. Blower 10 includes a control panel 22 with one or more buttons and preferably a display. Blower 10 includes a pressure sensor 24 to provide a signal to a controller 26 (e.g., CPU) for control of blower motor 14, in accordance with one or more control algorithms commercially available from ResMed, Inc.

Blower 10 is optionally provided with a selectively attachable and detachable humidifier unit 28 to form a humidifying system 29 that includes a tub 30 and one or more conduits 32, 34 that communicate with blower 10. Humidifier unit 28 may include structure as detailed in U.S. Published Patent Application No. 2004/0055597A1, incorporated by reference in its entirety. Humidifier unit 28 is in communication with controller 26, e.g., when conduits 32, 34 are attached to blower 10.

In one embodiment, the operation and/or performance of the humidifier unit 28 is tailored or profiled to suit the patient's specific humidification requirements. This in turn results in more efficient water usage, and allows the capacity of the tub 30 to be reduced. For example, the capacity of the tub 30 can be less than 400 mL, e.g., from 20 mL-400 mL or more preferably between 50 mL-200 mL. Of course, the volume capacity can be greater or less, depending on application. This reduced volume allows the overall size of the blower humidifier and/or assembly to be reduced, thereby removing design constraints and facilitating transport of the blower, e.g., during travel of the patient.

Profiling may be intermittent or profiled in accordance to a patient selectable profile or according to a selectable or semi/automated profile typical of the treatment session's ambient environment conditions.

Another embodiment may modify the delivery profile according to temperature of room over the course of a treatment session. The device may measure temperature versus time and predict what adjustments in profile are desirable to maintain efficient fluid/water use.

In another embodiment the profile may change over a set time period of treatment. For example, during an eight-hour treatment session, the profile begins at start of treatment and continues on to either end of session or a set time period on the device.

The above can obviously be used in combination with other embodiments such as watching average room temperature or even monitoring temperature changes over a period of hours, days, weeks, or months, and can modify the profile accordingly.

A profile may, for example, recognize that a typical bedroom tends to cool until the early hours of the morning where the temperature tends to stabilize before warming again by sunrise. Another profile that may be used may gradually reduce the humidity level during the course of the night in one simple form of the invention.

In embodiments, the invention may also postpone delivery until a period of the sleep session has passed. For example, a patient in the case of CPAP does not tend to go to sleep (beginning of treatment session) with dry airways. Their airways are probably going to dry later, say one hour into the night. Compared to conventional humidifiers used in OSA over eight-hour sessions, this feature alone can reduce humidification water volumes by one-eighth.

When implementing the delay feature, valves 35 a and 35 b can be used to divert the path of the air so as to by-pass the humidifier unit 28 via a by-pass conduit 35 c. The air path is schematically illustrated in FIG. 1 with a broken arrow 36. When shut, valves 35 a and 35 b form part of the respective walls of gas conduits within blower 10.

The invention in one preferred embodiment may cycle between switch on and off during the course of the night. These cycles can be regular, irregular, or otherwise controlled for numerous intervals and various durations using some smart electronic control. The switching off does not necessarily need to completely switch off, but may reduce in temperature during periods where less humidification is required. As mentioned, this reduces water usage but may also lead to reduced energy (power) consumption and/or reduced running costs. For example, humidifier unit 28 may include a heater element 27 to heat the volume of water. The heater element 27 can be controlled via controller 26.

A user's manually selectable version is also possible. For example, as shown in FIGS. 2 and 3, a patient may set the humidifier device from a menu including, e.g., a Square wave or a Sinusoidal wave which may be integrated into blower 10 or humidifier unit 28 in the form of a symbol on a dial or push button. The device then humidifies the air to a level according to these changing profiles over a treatment session. In the case of a Sinusoidal wave setting where the cycle starts as a ‘rise’, the humidifier level increases gradually to a maximum during the middle of a treatment session and gradually reduces to the end of the treatment session. The profile can be symmetrical or asymmetrical. Also, the delay feature described above can be used in conjunction with the Square and/or Sinusoidal wave, so that humidity is added only after treatment has commenced.

If the humidifier provides instantaneous humidification on demand, this profile may also be adapted on a patient breath-by-breath basis rather than over a full treatment session.

These profiles mentioned above can be any combination or variation of a wave/curve and/or stepped. It may also be automated to learn the ambient environmental conditions. For example, a temperature sensor 40 (FIG. 1) may monitor room temperature changes over the annual seasons and modify the profile further to gain maximum water/fluid use and efficiency. For example, during cooler months, the humidification profile may allow for longer humidification periods (during the switch on or higher heat cycle) but not allow as high a level so as to reduce condensation and maximize comfort for the patient.

Another embodiment may include a ‘fuzzy logic’ version where the user, with the assistance of the device's intelligence, provides an optimum humidification profile, which provides optimal comfort to the patient whilst maintaining efficient fluid/water usage. In this example, the patient may wake up and press one of three buttons, or select a dial setting, to indicate whether the level of humidification was “okay”, “too little” or “too much”. The device can then re-profile the delivery according to the patient's perceived comfort level. In this case, much of the actual profiling is automated.

Another embodiment of the invention considers two positive aspects of humidification and provides additional benefits. Current technology warms the patient breathing air. Warm air is considered more comfortable to breathe especially if the ambient temperature is relatively low. Secondly, humidifiers add moisture to the breathing air. The invention may profile the humidity level at a different rate to that of the air temperature. For example, according to the Sinusoidal wave setting example mentioned earlier, the device may maintain warm breathing air with minimal increased requirement at the middle of the treatment session. The humidity however may increase at an independent level relative to the temperature; for example, the humidity may increase much more than the temperature at the peak of the wave profile. This can again be selected by a patient according to their comfort requirements.

Any of the embodiments mentioned above may have an ability to transfer any ‘learned’ logic by memory storage media, or wireless communication (e.g. “Blue tooth” technology) so that the logic could be utilized by a physician, another user, or else simply because the patient intends to replace the device or upgrade to a newer model. Controller 26 may include a memory 26 b to facilitate data storage/transfer.

In a more mechanized embodiment of the invention, a simple valve that controls the humidified air entering the mainstream breathing air may be controlled by mechanical links. For example, as shown in FIG. 4, a rotating cam 42 that is profiled to control a valve 46 via mechanical linkage 48, thus producing staged delivery of humidified gas through a conduit 49 (which may be conduit 34 in FIG. 1). The cam profile can be such that the peak of the cam's lobe translates to largest valve opening and therefore greatest humidification level. The cam 42 could be designed to turn one revolution in one treatment session. The shape of the cam lobe determines the delivery profile. A bi-metallic spring may also be added to modify lift (generally reduce lift to reduce humidification as temperature decreases) and therefore forms a type of mechanical temperature compensation.

Further to the above embodiment, the profile could be mechanically adjustable by a user. For example, a number of selectable pins around the perimeter of a cam lobe could be push in or out to modify at what period of the session and by how much to lift the valve.

In another embodiment, the invention may also incorporate a switch or sensor device that switches off the humidifier should the treatment session be interrupted. For example, an OSA patient may get up in the middle of the night to go to the bathroom. This feature is designed to reduce water consumption further and also prevent condensation in the air delivery pipe, especially if the flow generator has stopped (ResMed's Smart Stop™ feature). It may also prevent the patient breathing in condensate when they return to bed, which in turn improves patient comfort.

Yet another embodiment of the invention includes a mask “rain-out” sensor 50 (FIG. 1) that does not require the use of humidity sensor like the prior art. An infrared emitter and detector in communication with controller 26, e.g., are placed at the bottom of the mask interface or location where condensation is likely to bead or pool. The mask frame wall in front of the side-by-side emitter/detector is transparent to infrared light. Under normal conditions, the detector does not see any infrared light. If significant water droplets develop (condensation) in front of the emitter/detector, the light reflects back to the detector and signifies condensation. The device may also use another type of visible or non-visible light emitter/detector combination.

The above feature applied to the invention may either reduce humidification or heating in response to “rain-out”, or otherwise it may modify the humidification delivery profiles as described earlier to improve patient comfort. Also by identifying “rain-out”, this may provide intelligence to the device's control that the ambient temperature is falling or the heating of the delivered air is too low to carry the current level of moisture.

One or more of the following advantages may be realized in accordance with preferred embodiments of the invention:

-   -   Humidifier that is smaller, easier to store or travel with.     -   A device that can be tailored (profiled) or set by a user to         suit their circumstances, needs or desires for comfort.     -   A profile humidifier may bridge the gap between inefficient         “Passover” (non-heated) humidifiers and fully featured heated         humidifiers that treat most dry airway ailments.     -   Potentially less complaints of “rain-out” or condensation as         patients may have adjusted their device to a high setting, only         to find that a cooling room creates increased condensation.     -   Ability to control, modify and fine-tune their patient's         therapy.     -   By minimizing humidity delivery when it is not necessary reduces         water usage and reservoir volume required, therefore reducing         device size.     -   Alleviates the size constraints on engineers for the OSA market         that is trending towards fewer design compromises to meet         comfort expectations.     -   Flow generators have already been reduced in size, whereas the         humidifier is about the same size as next generation flow         generators, if not larger. This concept gives users the         perception of even more compact dimension that is potentially         lighter and easier to transport.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the invention. For example, the above described preferred embodiments of the invention may be adapted to any humidification device whether to treat OSA or used in any gas breathing system. 

The invention claimed is:
 1. A humidifying system configured to humidify pressurized breathable gas, the humidifying system comprising: a housing configured to couple to a blower that is adapted to supply pressurized breathable gas to provide continuous positive airway pressure (CPAP) treatment to a patient; a tub adapted to hold a volume of water; a heater element to heat the volume of water; a temperature sensor to sense the ambient temperature; and a controller, wherein the controller is configured to control the heater element to provide a humidity profile during a treatment session, and a set point of the humidity profile is modified over at least a portion of the treatment session to maintain efficient use of the volume of water throughout the treatment session, wherein the set point of the humidity profile is modified as a function of the sensed ambient temperature and a measure of time.
 2. A humidifying system according to claim 1, wherein the humidity profile includes cycling the heater element on and off for predetermined periods of time during the treatment session.
 3. A humidifying system according to claim 1, wherein the humidity profile includes delaying turning on the heater element for a predetermined period of time at the beginning of the treatment session.
 4. A humidifying system according to claim 3, wherein the predetermined time is one hour.
 5. A humidifying system according to claim 1, wherein the humidity profile reduces the humidity level during the treatment session and the initial humidity level is determined based on the ambient temperature and the measure of time.
 6. A humidifying system according to claim 1, wherein the ambient temperature is sensed over a plurality of treatment sessions to determine the humidity profile.
 7. A humidifying system according to claim 1, wherein the humidity profile is determined from the sensed ambient temperature from one or more previous treatment sessions.
 8. A humidifying system according to claim 1, wherein the humidity profile is varied in response to the sensed ambient temperature of the current treatment session and the measure of time.
 9. A humidifying system according to claim 1, wherein time is measured over the entire treatment session.
 10. A humidifying system according to claim 1, wherein the measure of time counts down from a predetermined time value at the beginning of each treatment session.
 11. A humidifying system according to claim 10, wherein the predetermined time value is an average length of time of a treatment session.
 12. A humidifying system according to claim 11, wherein the average length of time of a treatment session is determined from a plurality of previous treatment sessions.
 13. A humidifying system according to claim 1, wherein the humidity profile is determined so that the humidity profile does not require a volume of water equal to or more than the volume of water available in the tub during a treatment session.
 14. An apparatus for providing continuous positive airway pressure (CPAP) treatment to a patient comprising: a blower adapted to provide a supply of pressurized breathable gas; a patient interface configured to deliver the supply of pressurized breathable gas to the patient; an air delivery conduit between the blower and the patient interface; and a humidifier unit comprising a humidifying system according to claim 1; wherein the humidifier unit includes at least one conduit in communication with the blower, the humidifier unit being configured to provide humidity to the pressurized breathable gas according to the humidity profile, and the humidity profile comprises a setting that causes the humidity to vary during the treatment session.
 15. An apparatus according to claim 14, further comprising a control panel to allow the humidity profile to be selected from a menu.
 16. An apparatus according to claim 15, wherein the menu includes at least one of a sinusoidal wave humidity profile, a square wave humidity profile and a combination thereof.
 17. An apparatus according to claim 14, wherein the humidity profile is configured to vary the humidity in response to changes in ambient environmental conditions.
 18. An apparatus according to claim 17, wherein the ambient environmental conditions include at least one of temperature and humidity.
 19. An apparatus according to claim 14, wherein the humidity profile is configured to cycle between switching the humidifier unit on and off during the treatment session.
 20. An apparatus according to claim 19, wherein the on and off cycles are configured to occur regularly throughout the treatment session.
 21. An apparatus according to claim 19, wherein the on and off cycles are configured to occur irregularly throughout the treatment session.
 22. An apparatus according to claim 19, wherein the off cycle is a period when the level of humidity provided is reduced compared to the level of humidity provided during the on cycle.
 23. An apparatus according to claim 14, wherein the humidity profile is configured to delay the supply of humidity for a predetermined period at the beginning of the treatment session.
 24. An apparatus according to claim 14, wherein the humidity profile is configured to reduce the level of humidity provided over time throughout the treatment session.
 25. An apparatus according to claim 14, wherein the humidity profile is configured to provide humidity for only a predetermined period of time of the treatment session.
 26. An apparatus according to claim 14, wherein the humidifier unit comprises two conduits in communication with the blower, one conduit adapted to supply the pressurised breathable gas to the humidifier and the other conduit adapted to supply the humidified pressurized breathable gas back to the blower for delivery to the air delivery conduit.
 27. An apparatus according to claim 26, wherein the blower further includes a diverting means to divert the path of the pressurized breathable gas to a by-pass means of the humidifier unit.
 28. An apparatus according to claim 27, wherein the diverting means includes a pair of valves to shut off the two conduits of the humidifier to prevent the pressurized breathable gas from entering the humidifier unit.
 29. An apparatus according to claim 14, wherein the patient interface further comprises a sensor configured to detect condensation.
 30. An apparatus according to claim 29, wherein the sensor includes at least one of an infrared emitter and a detector.
 31. An apparatus according to claim 29, wherein the humidity profile is configured to adjust the temperature of the breathable gas in response to a level of condensation sensed by the sensor.
 32. An apparatus according to claim 14, wherein the tub has a capacity in the range of 20 ml to 400 ml.
 33. An apparatus according to claim 32, wherein the tub has a capacity in the range of 50 ml to 200 ml.
 34. A humidifying system according to claim 1, wherein the humidity profile is modified as a function of a predicted ambient condition based on the measure of time.
 35. A humidifying system according to claim 1, wherein the humidity profile is modified as a function of a predicted humidification need of the patient based on the measure of time.
 36. A humidifying system configured to humidify pressurized breathable gas, the humidifying system comprising: a housing configured to couple to a blower that is adapted to supply pressurized breathable gas to provide continuous positive airway pressure (CPAP) treatment to a patient; a tub adapted to hold a volume of water; a heater element to heat the volume of water; a temperature sensor to sense the ambient temperature; and a controller configured to control the heater element based on a humidity profile that sets a target humidity level during the treatment session, the controller being further configured to modify the target humidity level of the humidity profile as a function of the sensed ambient temperature and a time monitored over at least a portion of a treatment session.
 37. A humidifying system according to claim 36, wherein the monitored time corresponds to at least one of: an amount of time that has elapsed since an initiation of the treatment session, time of day, and a time of year.
 38. A humidifying system according to claim 37, wherein the controller is configured to modify the humidity profile according to a change in the sensed ambient temperature over the course of the treatment session.
 39. A humidifying system according to claim 37, wherein a target humidity level of the humidity profile forms a sinusoidal wave over the course of the treatment session.
 40. A humidifying system according to claim 39, wherein the sinusoidal wave is symmetrical.
 41. A humidifying system according to claim 39, wherein the sinusoidal wave is asymmetrical.
 42. A humidifying system according to claim 37, wherein a target humidity level of the humidity profile forms a square wave over the course of the treatment session.
 43. A humidifying system according to claim 42, wherein the square wave is symmetrical.
 44. A humidifying system according to claim 42, wherein the square wave is asymmetrical.
 45. A humidifying system according to claim 37, wherein a target humidity level of the humidity profile forms a combination of at least two of a wave, a curve and a step over the course of the treatment session.
 46. A humidifying system according to claim 37, wherein the controller is configured to modify the humidity profile to reduce the humidity level during the treatment session and an initial target humidity level is determined based on the ambient temperature and the current time. 